1. Field of the Invention
The present invention relates to a magnetic recording medium with an improved magnetic layer coated thereon, the layer having an isobutylene oligomer as its essential lubricating agent.
2. Description of the Prior Art
In recent times, the characteristics required of a suitable magnetic recording medium such as a magnetic tape, a magnetic sheet, a magnetic disk, or the like have become much more severe. This is especially true in magnetic tape used for recording video signals where the so called "still picture" characteristic is important, and in magnetic tapes for recording audio signals as well as magnetic tapes used for measuring. In these instances, a repeating travelling characteristic and anti-abrasion properties become most important.
Heretofore, in order to improve the still picture characteristic, the repeating travelling characteristic, and the wear resistance characteristic, various binders, lubricants, additives and the like have been tried but particularly good results have not been obtained. Any lubricating agent must function without deteriorating the electromagnetic conversion characteristics, the head wear, the viscosity characteristics of the paints, and the like. Until the present time, the main objective in selecting a lubricant has been to smooth the travelling of the magnetic tape and to prevent the generation of Q-sounds and wow-flutters by reducing the friction factor existing during the low speed travel of the tape.
In the prior art, there have been various lubricants used in magnetic layers as for example higher fatty acids (for example, oleic acid, linoleic acid, ricinoleic acid, stearic acid, lauric acid, palmitic acid, capric acid, myristic acid, elaidic acid, stearolic acid, and the like which fatty acids contain 8 to 18 carbon atoms) and their fatty acid esters, or individual or mixtures of fatty acids of metallic salts, liquid paraffin, silicone oils, olive oil, and the like. Powdered materials such as graphite, carbon, molybdenum disulfide, boron nitride, tungsten disulfide, and powdered polyfluorovinyl polymers have also been tried.
The results obtained with olive oil, zinc stearate, ethyl stearate and silicone oils being used as lubricants have not proved satisfactory, as will be described in a succeeding portion of this specification.
When well known paraffin system and olefinic system lubricants are used in place of olive oil, the melting points of these lubricants being in the range from -5.degree. C. to 50.degree. C. are such that they cause "blooming" and therefore do not reduce the friction factor.
When a powdered lubricant is used, the volume in the magnetic layer which is occupied by the magnetic powders or particles is reduced. Therefore, the output from the magnetic tape is lowered and the uniform dispersion of the magnetic powders is disturbed, resulting in the production of a tape noise. Such a magnetic layer is no longer suitable for a magnetic tape for recording a short wave signal such as a video signal.
The most pertinent prior art with which the applicants are aware is a Japanese Patent Application Publication No. 6727/1967 which discloses a lubricant composed of a squalane having the empirical formula C.sub.30 H.sub.62 and the chemical name 2, 6, 10, 15, 19, 23-hexamethyl-tetracosane. However, this squalane is produced by hydrogenation of a squalene derived from the liver oil of a shark and is therefore quite expensive. This material can be produced by synthesis but is still quite expensive.